We have purchased the Memory Maker several times. The advantage is you get all of the on ride photos, character meet and greets (sometimes the lines are long, but sometimes you stumble upon one that it just forming, and can get a picture in just a few minutes) and family photos that include everyone in the family. Those family photos are more than worth the price for me, as I am usually the one manning the camera, so without Memory Maker, I either have to hand my camera to strangers to get our picture, or I get left out of them all.
The way it works is you created a My Disney Experience account for everyone in your traveling group, and link them all together through the friends and family. Once in the parks, you can have photos taken by any Photopass photographer you see. Ride photos and videos should link to your account through your Magic Band (if you see a wall of video screens with photos on your way out, take a moment and tap your magic band to claim your photo just to be sure you get it) any character meals where photos are taken will also be included. There are some fun Magic Shots that might also be included by certain Photopass Photographers.
You can view, and edit your photos using your My Disney Experience app on your mobile device, or by logging into My Disney Experience on the Disney World website. Your pictures will remain available on the website for 45 days from the day they were taken, so you should have plenty of time to make edits after you return home from your trip. Once you have made all of the edits you want, you can then download all of your photos. The download comes with a license that allows you to have them printed for your own use.
Over the years, I have used many of my photos for screen savers, and desktop wall papers on my computer, my phone, and my tablet. I also had a custom calendar printed this year through Vista Print using some of my Photopass pictures (and some of my own pictures as well.)
I hope this gives you a solid idea of what Memory Maker is. If you have further questions, feel free to ask. There will be a new thread here on the DIS soon, covering all of the important information about Photopass and Memory Maker.